Hydrocarbon fuels typically contain a complex mixture of hydrocarbons—molecules containing various configurations of hydrogen and carbon atoms. They may also contain various additives, including detergents, anti-icing agents, emulsifiers, corrosion inhibitors, dyes, deposit modifiers, and non-hydrocarbons such as oxygenates.
When such hydrocarbon fuels are combusted, a variety of pollutants are generated. These combustion products include ozone, particulates, carbon monoxide, nitrogen dioxide, sulfur dioxide, and lead. Both the U.S. Environmental Protection Agency (EPA) and the California Air Resources Board (CARB) have adopted ambient air quality standards directed to these pollutants. Both agencies have also adopted specifications for lower-emission gasolines.
The Phase 2 California Reformulated Gasoline (CaRFG2) regulations became operative in Mar. 1, 1996. Governor Davis signed Executive Order D-5-99 on Mar. 25, 1999, which directs the phase-out of methyl tertiary butyl ether (MTBE) in California's gasoline by Dec. 31, 2002. The Phase 3 California Reformulated Gasoline (CaRFG3) regulations were approved on Aug. 3, 2000, and became operative on Sep. 2, 2000. The CaRFG2 and CaRFG3 standards are presented in Table 1.
TABLE 1The California Reformulated Gasoline Phase 2 and Phase 3 SpecificationsFlat LimitsAveraging LimitsCap LimitsCaRFGCaRFGCaRFGCaRFGCaRFGCaRFGCaRFGCaRFGCaRFGPropertyPhase 1Phase 1Phase 1Phase 1Phase 2Phase 3Phase 1Phase 2Phase 3Reidn/a7.07.0 or 6.97.8n/an/an/a7.06.4–7.2VaporPressure(psi)Sulfurn/a40201513015n/a8060Content30(wt. ppm)Benzenen/a1.00.81.70.80.7n/a1.21.1Content(vol. %)Aromaticsn/a2525322222n/a3035Content(vol. %)Olefinsn/a6.06.09.64.04.0n/a10.010.0Content(vol. %)T50n/a210213212200203n/a220220(° F.)T90n/a300305329290295n/a330330(° F.)Oxygenn/a1.8–2.21.8–2.2n/an/an/an/a1.8–3.51.8–3.5Content  0–3.5  0–3.5(wt. %)MTBEn/an/aProhibitedn/an/an/an/an/aProhibitedand OtherOxygenates(other thanethanol)n/a = not applicable
Considerable effort has been expended by the major oil companies to formulate gasolines that comply with the EPA and CARB standards. The most common approach to formulating compliant gasolines involves adjusting refinery processes so as to produce a gasoline base fuel meeting the specifications set forth above. Such an approach suffers a number of drawbacks, including the high costs involved in reconfiguring a refinery process, possible negative effects on the quantity or quality of other refinery products, and the inflexibility associated with having to produce a compliant base gasoline.